Structural and functional maturation of distal femoral cartilage and bone during postnatal development and growth in humans and mice

A humanised rat model of osteosarcoma reveals ultrastructural differences between bone and mineralised tumour tissue

Current xenograft animal models fail to accurately replicate the complexity of human bone disease. To gain translatable and clinically valuable data from animal models, new in vivo models need to be developed that mimic pivotal aspects of human bone physiology as well as its diseased state. Above all, an advanced bone disease model should promote the development of new treatment strategies and facilitate the conduction of common clinical interventional procedures. Here we describe the development and characterisation of an orthotopic humanised tissue-engineered osteosarcoma (OS) model in a recently genetically engineered x-linked severe combined immunodeficient (X-SCID) rat. For the first time in a genetically modified rat, our results show the successful implementation of an orthotopic humanised tissue-engineered bone niche supporting the growth of a human OS cell line including its metastatic spread to the lung. Moreover, we studied the inter- and intraspecies differences in ultrastructural composition of bone and calcified tissue produced by the tumour, pointing to the crucial role of humanised animal models.

Cartilage degeneration is associated with activation of the PI3K/AKT signaling pathway in a growing rat experimental model of developmental trochlear dysplasia

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Established a new experimental rat model of the developmental trochlear dysplasia;

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Using the macroscopic morphological and micro-CT to assess trochlear dysplasia;

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Using Histological staining to investigate the cartilage degradation of the model;

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Investigated the relationship of the PI3K/AKT signaling pathway with trochlear dysplasia cartilage degeneration;

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Using immunohistochemistry and qPCR to investigate the PI3K/AKT and the marker of the cartilage degeneration.

Introduction

Trochlear dysplasia is a commonly encountered lower extremity deformity in humans. However, the molecular mechanism of cartilage degeneration in trochlear dysplasia is unclear thus far.

Objectives

The PI3K/AKT signaling pathway is known to be important for regulating the pathophysiology of cartilage degeneration. The aim of this study was to investigate the relationship of the PI3K/AKT signaling pathway with trochlear dysplasia cartilage degeneration.

Methods

In total, 120 female Sprague-Dawley rats (4 weeks of age) were randomly separated into control and experimental groups. Distal femurs were isolated from the experimental group at 4, 8, and 12 weeks after surgery; they were isolated from the control group at the same time points. Micro-computed tomography and histological examination were performed to investigate trochlear anatomy and changes in trochlear cartilage. Subsequently, expression patterns of PI3K/AKT, TGFβ1, and ADAMTS-4 in cartilage were investigated by immunohistochemistry and quantitative polymerase chain reaction.

Results

In the experimental group, the trochlear dysplasia model was successfully established at 8 weeks after surgery. Moreover, cartilage degeneration was observed beginning at 8 weeks after surgery, with higher protein and mRNA expression levels of PI3K/AKT, TGFβ1, and ADAMTS-4, relative to the control group.

Conclusion

Patellar instability might lead to trochlear dysplasia in growing rats. Moreover, trochlear dysplasia may cause patellofemoral osteoarthritis; cartilage degeneration in trochlear dysplasia might be associated with activation of the PI3K/AKT signaling pathway. These results provide insights regarding the high incidence of osteoarthritis in patients with trochlear dysplasia. However, more research is needed to clarify the underlying mechanisms.

Frequent, quantitative bone planar scintigraphy for determination of bone anabolism in growing mice

Background

To provide insight into bone turnover, quantitative measurements of bone remodeling are required. Radionuclide studies are widely used in clinical care, but have been rarely used in the exploration of the bone in preclinical studies. We describe a bone planar scintigraphy method for frequent assessment of bone activity in mice across the growing period. Since repeated venous radiotracer injections are hardly feasible in mice, we investigated the subcutaneous route.

Methods

Repeated ^99mTc-hydroxymethylene diphosphonate (HMDP) tracer bone planar scintigraphy studies of the knee region and µCT to measure femur growth rate were performed in eight mice between week 6 and week 27 of life, i.e., during their growth period. Three independent investigators assessed the regions of interest (ROI). An index was calculated based on the counts in knees ROI (normalized by pixels and seconds), corrected for the activity administered, the decay between administration and imaging, and individual weights.

Results

A total of 93 scintigraphy studies and 85 µCT were performed. Repeated subcutaneous tracer injections were well tolerated and allowed for adequate radionuclide studies. Mean scintigraphic indexes in the knees ROI decreased from 87.4 ± 2.6 × 10⁻⁶ counts s⁻¹ pixel⁻¹ MBq⁻¹ g⁻¹ at week 6 to 15.0 ± 3.3 × 10⁻⁶ counts s⁻¹ pixel⁻¹ MBq⁻¹ g⁻¹ at week 27. The time constant of the fitted exponential decay was equal to 23.5 days. As control mean femur length assessed by µCT increased from 12.2 ± 0.8 mm at week 6 to 15.8 ± 0.2 mm at week 22. The time constant of the fitted Gompertz law was equal to 26.7 days. A correlation index of −0.97 was found between femur growth and decrease of bone tracer activity count between week 6 and 24.

Conclusion

This methodological study demonstrates the potential of repeated bone planar scintigraphy in growing mice, with subcutaneous route for tracer administration, for quantitative assessment of bone remodeling.

Comparative anatomy and morphology of the knee in translational models for articular cartilage disorders. Part II: Small animals

BACKGROUND

Small animal models are critical to model the complex disease mechanisms affecting a functional joint leading to articular cartilage disorders. They are advantageous for several reasons and significantly contributed to the understanding of the mechanisms of cartilage diseases among which osteoarthritis.

METHODS

Literature search in Pubmed.

RESULTS AND DISCUSSION

This narrative review summarizes the most relevant anatomical structural and functional characteristics of the knee (stifle) joints of the major small animal species, including mice, rats, guinea pigs, and rabbits compared with humans. Specific characteristics of each species, including kinematical gait parameters are provided and compared with the human situation. When placed in a proper context respecting their challenges and limitations, small animal models are important and appropriate models for articular cartilage disorders.

The dysplastic trochlear sulcus due to the insufficient patellar stress in growing rats

BACKGROUND

Developmental factors were assumed to be the key factors that influenced the morphology of femoral trochlea. This study investigated the effects of insufficient patellar stress after birth on the morphological development of the femoral trochlea. Effects of insufficient patellar stress on femoral trochlea were investigated using surgical induced patellectomy and patellar dislocation in growing rat model.

METHODS

In this study, two experimental groups and one sham group (SG) were established. Thirty-six Wistar rats (female, 28 days of age) were randomly assigned to three groups. The patellectomy group (PG), rats underwent the patellectomy in this group. The dislocation group (DG), rats underwent the surgery-induced patellar dislocation. Histological staining (Safranin-O and fast green), Micro-computed tomographic (Micro-CT) analysis in two experimental endpoints (3, 12 weeks postoperatively) were selected to evaluate morphological changes of the femoral trochlea.

RESULTS

Articular cartilage on the trochlear sulcus was remodeled at 3 weeks after the surgery, and degenerated at 12 weeks through the histological staining. The femoral trochlear angle (FTA) did not show a significant difference at 3 week between the experimental groups and the sham group (PG vs SG P = 0.38, DG vs SG p = 0.05), but the FTA was significantly increased in experimental groups at 12 weeks(PG vs SG P = 0.001, DG vs SG p = 0.005). The Bone volume density (BV/TV), Trabecular number (Tb.N) under the trochlea groove were significantly reduced at 3 weeks postoperatively in the experimental groups (PG vs SG p = 0.001, DG vs SG p = 0.002). No significant difference was found in BV/TV and Tb. N among the three groups at 12 weeks postoperatively.

CONCLUSION

Surgical induced patellectomy and patellar dislocation leads to the dysplastic trochlear sulcus in growing rats. Besides the bone morphology of trochlear sulcus, the articular cartilage and subchondral trabecula under the trochlear sulcus were remodeled early stage after the surgery.

Novel model for the induction of postnatal murine hip deformity

Acetabular dysplasia is a common, multi-etiological, pre-osteoarthritic (OA) feature that can lead to pain and instability of the young adult hip. Despite the clinical significance of acetabular dysplasia, there is a paucity of small animal models to investigate structural and functional changes that mediate morphology of the dysplastic hip and drive the subsequent OA cascade. Utilizing a novel murine model developed in our laboratory, this study investigated the role of surgically induced unilateral instability of the postnatal hip on the initiation and progression of acetabular dysplasia and impingement up to 8-weeks post-injury. C57BL6 mice were used to develop titrated levels of hip instability (i.e., mild, moderate, and severe instabillity or femoral head resection) at weaning. Joint shape, acetabular coverage, histomorphology, and statistical shape modeling were used to assess quality of the hip following 8 weeks of destabilization. Acetabular coverage was reduced following severe, but not moderate, instability. Moderate instability induced lateralization of the femur without dislocation, whereas severe instability led to complete dislocation and pseudoacetabulae formation. Mild instability did not result in morphological changes to the hip. Removal of the femoral head led to reduced hip joint space volume. These data support the notion that hip instability, driven by mechanical loss-of-function of soft connective tissue, can induce morphometric changes in the growing mouse hip. This work developed a new mouse model to study hip health in the murine adolescent hip and is a useful tool for investigating the mechanical and structural adaptations to hip instability during growth. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

3-dimensional metrics of proximal femoral shape deformities in Legg-Calvé-Perthes disease and slipped capital femoral epiphysis

Legg-Calvé-Perthes disease (LCPD) and slipped capital femoral epiphysis (SCFE) are two common pediatric hip disorders that affect the 3-dimensional shape and function of the proximal femur. This study applied the principles of continuum mechanics to statistical shape modeling (SSM) and determined 3-D metrics for the evaluation of shape deformations in normal growth, LCPD, and SCFE. CT scans were obtained from 32 patients with asymptomatic, LCPD, and SCFE hips ((0.5-0.9 mm)² in-plane resolution, 0.63 mm slice thickness). SSM was performed on segmented proximal femoral surfaces, and shape deformations were described by surface displacement, strain, and growth plate angle metrics. Asymptomatic normal femurs underwent coordinated, growth-associated surface displacements and anisotropic strains that were site-specific and highest at the greater trochanter. After size- and age-based shape adjustment, LCPD femurs exhibited large displacements and surface strains in the femoral head and neck, with associated changes in femoral head growth plate angles. Mild SCFE femurs had contracted femoral neck surfaces, and surface displacements in all regions tended to increase with severity of slip. The results of this paper provide new 3-D metrics for characterizing the shape and biomechanics of the proximal femur. Statement of Clinical Significance: Quantitative 3-D metrics of shape may be useful for understanding and monitoring disease progression, identifying target regions for shape modulation therapies, and objectively evaluating the success of such therapies. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1526-1535, 2018.

Heat-Induced Limb Length Asymmetry Has Functional Impact on Weight Bearing in Mouse Hindlimbs

Limb length inequality results from many types of musculoskeletal disorders. Asymmetric weight bearing from a limb length discrepancy of less than 2% can have debilitating consequences such as back problems and early-onset osteoarthritis. Existing treatments include invasive surgeries and/or drug regimens that are often only partially effective. As a noninvasive alternative, we previously developed a once daily limb-heating model using targeted heat on one side of the body for 2 weeks to unilaterally increase bone length by up to 1.5% in growing mice. In this study, we applied heat for 1 week to determine whether these small differences in limb length are functionally significant, assessed by changes in hindlimb weight bearing. We tested the hypothesis that heat-induced limb length asymmetry has a functional impact on weight bearing in mouse hindlimbs. Female 3-week-old C57BL/6 mice (N = 12 total) were treated with targeted intermittent heat for 7 days (40 C for 40 min/day). High-resolution x-ray (N = 6) and hindlimb weight bearing data (N = 8) were acquired at the start and end of the experiments. There were no significant left-right differences in starting tibial length or hindlimb weight bearing. After 1-week heat exposure, tibiae (t = 7.7, p < 0.001) and femora (t = 11.5, p < 0.001) were ~1 and 1.4% longer, respectively, on the heat-treated sides (40 C) compared to the non-treated contralateral sides (30 C). Tibial elongation rate was over 6% greater (t = 5.19, p < 0.001). Hindlimb weight bearing was nearly 20% greater (t = 11.9, p < 0.001) and significantly correlated with the increase in tibial elongation rate on the heat-treated side (R² = 0.82, p < 0.01). These results support the hypothesis that even a small limb length discrepancy can cause imbalanced weight distribution in healthy mice. The increase in bone elongation rate generated by localized heat could be a way to equalize limb length and weight bearing asymmetry caused by disease or trauma, leading to new approaches with better outcomes by using heat to lengthen limbs and reduce costly side effects of more invasive interventions.

First and second order stereology of hyaline cartilage: Application on mice femoral cartilage

Stereological techniques could be considered in research on cartilage to obtain quantitative data. The present study aimed to explain application of the first- and second-order stereological methods on articular cartilage of mice and the methods applied on the mice exposed to cadmium (Cd). The distal femoral articular cartilage of BALB/c mice (control and Cd-treated) was removed. Then, volume and surface area of the cartilage and number of chondrocytes were estimated using Cavalieri and optical dissector techniques on isotropic uniform random sections. Pair-correlation function [g(r)] and cross-correlation function were calculated to express the spatial arrangement of chondrocytes-chondrocytes and chondrocytes-matrix (chondrocyte clustering/dispersing), respectively. The mean±standard deviation of the cartilage volume, surface area, and thickness were 1.4±0.1mm³, 26.2±5.4mm², and 52.8±6.7μm, respectively. Besides, the mean number of chondrocytes was 680±200 (×10³). The cartilage volume, cartilage surface area, and number of chondrocytes were respectively reduced by 25%, 27%, and 27% in the Cd-treated mice in comparison to the control animals (p<0.03). Estimates of g(r) for the cells and matrix against the dipole distances, r, have been plotted. This plot showed that the chondrocytes and the matrix were neither dispersed nor clustered in the two study groups. Application of design-based stereological methods and also evaluation of spatial arrangement of the cartilage components carried potential advantages for investigating the cartilage in different joint conditions. Chondrocyte clustering/dispersing and cellularity can be evaluated in cartilage assessment in normal or abnormal situations.

Unilateral heat accelerates bone elongation and lengthens extremities of growing mice

Linear growth failure results from a broad spectrum of systemic and local disorders that can generate chronic musculoskeletal disability. Current bone lengthening protocols involve invasive surgeries or drug regimens, which are only partially effective. Exposure to warm ambient temperature during growth increases limb length, suggesting that targeted heat could noninvasively enhance bone elongation. We tested the hypothesis that daily heat exposure on one side of the body unilaterally increases femoral and tibial lengths. Mice (N = 20) were treated with 40 °C unilateral heat for 40 min/day for 14 days post-weaning. Non-treated mice (N = 6) served as controls. Unilateral increases in ear (8.8%), hindfoot (3.5%), femoral (1.3%), and tibial (1.5%) lengths were obtained. Tibial elongation rate was > 12% greater (15 μm/day) on the heat-treated side. Extremity lengthening correlated with temperature during treatment. Body mass and humeral length were unaffected. To test whether differences persisted in adults, mice were examined 7-weeks post-treatment. Ear area, hindfoot, femoral, and tibial lengths were still significantly increased ∼6%, 3.5%, 1%, and 1%, respectively, on the heat-treated side. Left-right differences were absent in non-treated controls, ruling out inherent side asymmetry. This model is important for designing noninvasive heat-based therapies to potentially combat a range of debilitating growth impediments in children.

TAK1 regulates SOX9 expression in chondrocytes and is essential for postnatal development of the growth plate and articular cartilages

TAK1 is a MAP3K that mediates non-canonical TGF-β and BMP signaling. During the embryonic period, TAK1 is essential for cartilage and joint development as deletion of Tak1 in chondro-osteo progenitor cells leads to severe chondrodysplasia with defects in both chondrocyte proliferation and maturation. We have investigated the role of TAK1 in committed chondrocytes during early postnatal development. Using the Col2a1-CreER(T2); Tak1(f/f) mouse model, we induced deletion of Tak1 at postnatal day 7 and characterized the skeletal phenotypes of these mice at 1 and 3 months of age. Mice with chondrocyte-specific Tak1 deletion exhibited severe growth retardation and reduced proteoglycan and type II collagen content in the extracellular matrix of the articular cartilage. We found reduced Col2a1 and Acan expression, but increased Mmp13 and Adamts5 expression, in Tak1-deficient chondrocytes along with reduced expression of the SOX trio of transcription factors, SOX9, SOX5 and SOX6. In vitro, BMP2 stimulated Sox9 gene expression and Sox9 promoter activity. These effects were reduced; however, following Tak1 deletion or treatment with a TAK1 kinase inhibitor. TAK1 affects both canonical and non-canonical BMP signal transduction and we found that both of these pathways contribute to BMP2-mediated Sox9 promoter activation. Additionally, we found that ATF2 directly binds the Sox9 promoter in response to BMP signaling and that this effect is dependent upon TAK1 kinase activity. These novel findings establish that TAK1 contributes to BMP2-mediated Sox9 gene expression and is essential for the postnatal development of normal growth plate and articular cartilages.